Heat exchanger and method of manufacturing the same

ABSTRACT

A heat exchanger includes at least one tube provided with an inner fin in a fluid passage which is defined by the tube therein and has a substantially ellipse-shaped cross section. A plate member for constructing the tube has two edge portions, which overlap each other and are integrally joined at a single joint disposed at a major-axis direction end of the tube. The inner fin is arranged in the tube before the forming of the joint, thus improving an arrangement performance of the inner fin. Moreover, there exists the single joint positioned at the one end of the tube so that a joint reliability of the tube is enhanced.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on a Japanese Patent Application No. 2004-309939 filed on Oct. 25, 2004, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger and a method of manufacturing the heat exchanger, in which a tube is provided with an inner fin therein.

BACKGROUND OF THE INVENTION

Generally, an inner fin can be arranged in a tube of a heat exchanger, for example, referring to JP-2003-28586A. In the manufacture of the heat exchanger, a pair of plates having a substantially ⊃-shaped cross section are confronted with each other to be engaged, while the inner fin is positioned therebetween. Thereafter, a joining of the two plates and a joining of the inner fin to the two plates are performed by brazing through a brazing material paste, which is applied to surfaces of the two plates. Thus, the tube in which the inner fin is joined to an inner surface thereof is formed.

In this case, the plates (plate members) are combined to construct the tube, considering an arrangement performance of the inner fin in the tube. However, because the flow of the brazing material in the brazing is not satisfactory at the position where there exists a relatively large gap between the plates due to a plate distortion or the like, a joint defect easily occurs. Thus, a fluid leakage from the heat exchanger may be caused.

SUMMARY OF THE INVENTION

In view of the above-described disadvantage, it is an object of the present invention to provide a heat exchanger and a manufacturing method thereof, to improve a joint reliability of a tube of the heat exchanger while an arrangement performance of an inner fin in the tube can be maintained.

According to an aspect of the present invention, a heat exchanger includes at least one tube and at least one inner fin. The tube is constructed of a plate member, and defines therein a fluid passage having a substantially ellipse-shaped cross section. The inner fin is arranged in the tube and joined thereto by brazing. The tube has a single joint, through which the plate member is integrally joined. The joint is continuous in a longitudinal direction of the tube and positioned at a major-axis direction end of the tube.

Thus, the inner fin can be inserted in the tube from the side of this major-axis direction end, before the joint is formed. Moreover, because the tube is provided with the single joint which can be positioned at the one major-axis direction end, a joint reliability of the tube is enhanced.

According to another aspect of the present invention, a method of manufacturing a heat exchanger is provided. The heat exchanger has at least one tube, which is constructed of a plate member and provided with an inner fins therein. The method includes a forming process for bending the plate member to form a tube body which defines therein a fluid passage having a substantially ellipse-shaped cross section, a first joining process for integrally joining the tube body to form a tube, an arranging process for disposing the inner fin before the forming process at a position where the fluid passage defined by the tube body is to be formed, and a second joining process for integrally joining the inner fin to an inner surface of the tube by brazing. At the forming process, two edge portions of the plate member are contacted with each other in a longitudinal direction of the tube body, and positioned at a major-axis direction end of the tube body. At the first joining process, the two edge portions of the plate member are joined to each other.

Thus, the above-described heat exchanger can be manufactured. That is, the inner fin can be inserted in the tube from the side of the major-axis direction end, before the joint is formed. Moreover, the tube can be formed to have the single joint which is positioned at the one major-axis direction end. Therefore, the joint reliability of the tube can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings, in which:

FIG. 1 is a schematic front view showing a whole construction of a heat exchanger according to a first embodiment of the present invention;

FIG. 2 is a vertical sectional view taken along a line II-II in FIG. 1;

FIG. 3 is cross-sectional view showing an arranging process of an inner fin in a plate member according to the first embodiment;

FIG. 4 is cross-sectional view showing a forming process of a tube body according to the first embodiment;

FIG. 5 is a partially enlarged sectional view of FIG. 4;

FIG. 6 is a partially enlarged sectional view of FIG. 2 to show a joining process of the tube body and a joining process of the inner fin according to the first embodiment;

FIG. 7 is a partially sectional view showing a forming process of a tube body of a heat exchanger according to a second embodiment of the present invention; and

FIG. 8 is a partially sectional view showing a joining process of the tube body according to the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment

A first embodiment of the present invention will be described with reference to FIGS. 1-6. Referring to FIG. 1, a heat exchanger 100 (e.g., intercooler) is provided with a core member 120 and a pair of header tanks 110, which are respectively mounted at two ends (of longitudinal direction of tube 122 described later) of the core member 120. Each of the header tanks 110 has a hollow construction, and includes a core plate 111 and a tank portion 112 which are made of a copper alloy or the like and integrally joined by welding or brazing, for example.

One (e.g., at right side in FIG. 1) of the header tanks 110 is provided with an inlet joint 113 communicated with the interior of the one header tank 110. The other of the header tanks 110 (e.g., at left side in FIG. 1) is provided with an outlet joint 114 communicated with the interior of the other header tank 110. The inlet joint 113 can be connected with a discharge side of a supercharger (not shown), and the outlet joint 114 can be connected with a suction side of an engine (not shown), for example.

The inlet joint 113 is an introduction port, through which fluid (e.g., air) is introduced into the header tank 110. The outlet joint 114 is a discharge port, through which the fluid is discharged from the header tank 110.

Each of the header tanks 110 tapers from one longitudinal-direction end thereof (where joint 113 or 114 is disposed) toward other longitudinal-direction end thereof. That is, the cross section area of the interior space of the header tank 110 becomes smaller from the one end toward the other end thereof, so that the fluid evenly flows through the multiple tubes 122 of the core member 120.

Moreover, the header tanks 110 are respectively provided with at least a stay 130, which is arranged at an outer side (i.e., opposite side to core member 120) of the header tank 110 for an attachment of the intercooler 100 to a vehicle, for example.

The core member 120 includes multiple fins 121 for radiating heat and the multiple flat tubes 122. The fins 121 and the tubes 122 are alternately stacked (laminated). That is, each of the tubes 122 is sandwiched between the adjacent fins 121. Two side plates 124, being reinforce members, are respectively mounted (e.g., by brazing) at further outer sides of the two fins 121 which are disposed at the outmost sides of a stacking direction of the fins 121. In this case, the stacking direction of the fins 121 (tube 122) is perpendicular to the longitudinal direction of the fin 121 (tube 122).

The header tanks 110 are respectively attached to the two longitudinal-direction ends of the tube 122, and extend in a direction (i.e., longitudinal direction thereof) that intersects the longitudinal direction of the tube 122. The two ends of the tube 122 are respectively inserted into penetration holes (not shown) formed at the core plates 111 of the two header tanks 110, and integrated with the core plates 111 by brazing or the like.

FIG. 2 shows a thickness-direction sectional view of the tube 122. In FIG. 2, the up-down direction indicates a thickness direction of the tube 122, and the right-left direction indicates a width direction of the tube 122.

The flat tube 122 includes a pair of plane portions 122 a, a first bend portion 122 b and a second bend portion 122 c, to define therein a fluid passage having a thickness-direction section with a substantial ellipse shape, as shown in FIG. 2. The two plane portions 122 a are disposed parallel to each other and extend in the longitudinal direction of the tube 122. The two bend portions 122 b and 122 c convex outward, and are respectively disposed at two width-direction ends of the tube 122. The width direction of the tube 122 corresponds to the major axis direction of the substantial ellipse-shaped section of the tube 122.

The tube 122 is formed by a plate member 122B having a first edge portion 122 d and a second edge portion 122 e, which are arranged at the first bend portion 122 b of the tube 122 and overlap each other to be integrally joined by brazing or the like. The edge portions 122 d and 122 e extend in the longitudinal direction of the plate member 122B (tube 122).

In this case, the first bend portion 122 b where the first edge portion 122 d and the second edge portion 122 e overlap each other is disposed at an upstream side (e.g., back side of paper of FIG. 1) of an exterior fluid (e.g., air) which flows through the core member 120 including the tubes 122.

The tube 122 is provided with an inner fin 123 therein, which is joined to an inner surface of the tube 122 by brazing or the like. On the other hand, the heat-radiating fin 121 is joined to an outer surface of the tube 122 by brazing, for example.

The heat-radiating fin 121 and the inner fin 123 are made of copper or the like having an adequate heat conductivity. The tube 122 (formed by plate member 122B) and the side plate 124 are made of a copper alloy or the like having an adequate heat conductivity and a satisfactorily strength. The tube 122 can be also made of cupper.

The components of the core member 120 and the core plates 111 of the header tanks 110 are temporarily assembled, then integrally joined by brazing through a paste-like or foil-like brazing material, which is beforehand applied to the preferable positions of the components of the core member 120 and the core plates 111. Thereafter, the tank portion 112 is joined to the core plate 111. Thus, the intercooler 100 is constructed.

The tube 122 of the intercooler 100 is set to be relatively long in the longitudinal direction thereof. For example, the width (in right-left direction in FIG. 2) of the tube 122 can be about 60 mm. The length (in right-left direction in FIG. 1) of the tube 122 can be 800 mm or so. The thickness of the tube 122 (in up-down direction in FIG. 2) can be about 6 mm.

Next, the forming of the tube 122 and the inner fin 123, and the joining thereof will be described.

Referring to FIG. 3 showing an arranging process (disposing process) of the inner fin 123 in the plate member 122B, the inner fin 123 which is a separated component with respect to the plate member 122B is positioned in the plate member 122B having a substantially V-shaped cross section. The inner fin 123 has a substantial wave shape, for example. The thickness of the inner fin 123 is smaller than that of the plate member 122B. Thus, the total surface area in the plate member 122B can be enlarged, while the weight increase and the resistance (against fluid flowing therein) increase can be restricted.

At this state (referring to FIG. 3), the arc-shaped second bend portion 122 c is formed at the plate member 122B to connect the two plane portions 122 a, while the first edge portion 122 d is separated from the second edge portion 122 e. The first edge portion 122 d can be formed to have a substantial arc shape, and the second edge portion 122 e can be formed to have a substantial “L” shape. The first edge portion 122 d and the second edge portion 122 e are spaced from each other to form an opening therebetween, through which the inner fin 123 is inserted in the substantially V-shaped plate member 122B.

Moreover, in this case, a paste-like copper brazing material is applied to the inner surface of the plate member 122B, thus forming a paste layer 125 (brazing-material paste layer). Alternatively, a foil-like brazing material (i.e., brazing sheet) can be also provided for the inner surface of the plate member 122B.

In this case, the paste-like brazing material which is applied to the plate member 122B contains 89% Sn—P—Ni—Cu alloy (as brazing-material composition) by weight, 10% aliphatic hydrocarbon and alicyclic hydrocarbon (organic composition including binder and solvent) by weight, and 1% polyisobutylene by weight, for example.

According to this embodiment, as described above, the tube 122 has a long flat shape to be relatively long in the longitudinal direction thereof. Because the inner fin 123 is inserted into the plate member 122B (constructing tube 122) having the V-shaped cross section through the opening between the first and second edge portions 122 d and 122 e, a break (fracture) of the paste layer 125 can be substantially restricted as compared with the case where an inner fin is inserted into a tube which is formed to have a flat cylinder shape.

When a base material (i.e., material to be joined) is copper, it is difficult to clad the brazing material to the surface of the copper brazing material (as compared with the case where base material is aluminum alloy), so that the brazing material is readily stripped off the base material due to a contact or the like. Therefore, in this case, the prevention of the break of the brazing material paste layer 125 is a considerable merit.

FIG. 4 shows a forming process of a tube body 122A constructed by the plate member 122B. After the inner fin 123 is inserted in the plate member 122B having the V-shaped cross section, the second edge portion 122 e is revolved toward the first edge portion 122 d to overlap the first edge portion 122 d, referring to FIG. 4. In this case, the second edge portion 122 e is plastically deformed by swaging or the like, to be capable of coinciding with the outer surface of the first edge portion 122 d. Then, the arc-shaped bend portion 122 b is constructed by the second edge portion 122 e and the first edge portion 122 d.

As shown in FIG. 5 which is a partially enlarged sectional view of FIG. 4, in the above-described swaging process, a tip 122 g of the second edge portion 122 e is plastically deformed to be prolonged, thus having a taper shape. Therefore, a level difference can be prevented from forming at the tip 122 g, so that an outer surface of the first bend portion 122 b is smoothed. Thus, the tube body 122A having a simple ellipse outer shape is formed by the plate member 122B.

Moreover, in the above-described swaging process, the two plane portions 122 a of the plate member 122B are moved (approached) toward each other to become parallel. Therefore, the wave-shaped inner fin 123 which is arranged inside the plate member 122B is sandwiched by the two plane portions 122 a, so that crest portions (peak portions) of the wave-shaped inner fin 123 can closely contact the inner surfaces of the plane portions 122 a.

The two edge portions 122 d and 122 e of the plate member 122B are temporarily fixed at the bend portion 122 b, to form the tube body 122A having a substantially ellipse-shaped cross section. The bend portion 122 b is disposed at the one major-axis direction end of the tube body 122A. After the formation of the tube body 122A, the brazing material layer is provided at the outer surfaces of the plane portions 122 a. The heat-radiating fins 121, the side plates 124 and the core plates 111 are temporarily assembled and fixed to each other.

In this case, because the tube body 122A has the simple ellipse shape and the penetration hole (not shown) of the core plate 111 is also formed to have an simple ellipse shape, the longitudinal-direction ends of the tube 122A can be engaged with the core plates 111 without a large clearance (gap).

The components of the tube body 122A in which the inner fin 123 is disposed are temporarily assembled and fixed to each other to construct an assembly. Thereafter, the assembly is disposed in a furnace to be heated at a temperature equal to or below 680° C. or so.

An inert gas and a reduction composition such as hydrogen gas are circulated in the furnace, and flow through the interior of the assembly. Thus, oxides at the components can be removed (reduced), and oxidation of the components can be prevented by the reduction composition. Alternatively, the inert gas without including the reduction composition can be also provided in the furnace, when only the oxidation prevention is aimed.

The brazing material paste layer 125 will melt when being provided with a heat temperature equal to or beyond 600° C. Referring to FIG. 2, the melted brazing material will flow to the vicinity portions among the different components of the tube body 122A. Thus, the first edge portion 122 d and the second edge portion 122 e of the tube body 122A are integrally joined by brazing, so that the tube 122 is formed. In this case, the inner fin 123 is joined to the inner surface of the tube 122 and the heat-radiating fin 121 is joined to the outer surface of the tube 122 by brazing.

FIG. 6 shows the joining process of the tube body 122A and that of the inner fin 123, which can be performed meanwhile. In the furnace, the tube body 122A is arranged so that the side of the bend portion 122 b is positioned at the lower side. Referring to FIG. 6, the brazing material which has not been used for the brazing of the inner fin 123 drops due to the weight thereof to be accumulated at a tip 122f of the first edge portion 122 d, thus improving a fillet formation. Therefore, the strength of a joint 125 a between the first edge portion 122 d and the second edge portion 122 e is increased.

According to this embodiment, at the tube 122 of the intercooler 100, only the side of the first bend portion 122 b is provided with the joint 125 a that is continuous in the longitudinal direction of the tube 122. The inner fin 123 is arranged in the tube 122 before the joint 125 a is formed. Thus, the arrangement performance of the inner fin 123 is improved. Because there is only the single joint 125 a at the tube 122, the joint reliability of the tube 122 can be bettered.

As a contrast, in the case where the tube is provided with the two joints respectively positioned at two ends of the tube of the width-direction (i.e., major axis direction of ellipse-shaped cross section of tube) thereof, the brazing material at the joint of the one end of an upper side will drop downward when the other end is disposed at a lower side in brazing. Thus, a brazing failure is easily caused at the joint of the upper side.

According to this embodiment, there exists the single joint 125 a which is positioned at the one end (where first bend portion 122 b is positioned) of the tube 122 of the major-axis direction thereof. The one end of the tube 122 can be arranged at the lower side in brazing. Thus, the joint reliability of brazing can be further improved.

Moreover, the plate member 122B is constructed to be twofold at the joint 125 a. That is, the first edge portion 122 d overlaps the second edge portion 122 e. Thus, the joint area of the joint 125 a is increased. Therefore, the joint reliability is enhanced, and the strength of the bend portion 122 b where the joint 125 is positioned is heightened. Because the bend portion 122 b having the higher strength is positioned at the upstream side of the exterior fluid of the intercooler 100, the tube 122 is sturdy (strong) against the damage even when stones, sands or the like from the exterior collide with the tube 122.

Furthermore, according to this embodiment, the plate member 122B is overlapped at the joint 125 a, and the outer surface of the plate member 122B is smoothed in the swaging process. The penetration hole (not shown) of the core plate 111 is formed to have the simple ellipse shape. Thus, the accuracy of the engagement of the tube 122 with the core plate 111 can be improved. Therefore, the fluid leakage from the joint between the tube 122 and the core plate 111 can be restricted.

Second Embodiment

A second embodiment of the present invention will be described referring to FIGS. 7 and 8. In this case, a joint 225 at the bend portion 122 b of the tube 122 is formed by welding.

In the second embodiment, the forming process of the tube body 122A is performed after the arranging process of the inner fin 123 is performed. That is the same with the above-described first embodiment.

Referring to FIG. 7, in the forming process of the tube body 122A, the second edge portion 122 e is revolved toward the first edge portion 122 d (i.e., toward right side in FIG. 7), so that the second edge portion 122 e contacts the first edge portion 122 e. Then, the first edge portion 122 d is temporarily fixed to the second edge portion 122 e to construct the arc-shaped bend portion 122 b. In this case, a tip 122 g of the second edge portion 122 e is not prolonged (deformed).

Then, referring to FIG. 8, the joining process of the tube body 122A is performed. In this case, the tip 122 g of the second edge portion 122 e is joined to the first edge portion 122 d by laser-welding or the like to form the joint 225, after the two edge portions 122 d and 122 e are temporarily fixed to each other as shown in FIG. 7. The first edge portion 122 d is positioned at the inner side of the second edge portion 122 e. Thus, the tube 122 is formed as shown in FIG. 8.

In this case, the outer surface of the first bend portion 122 b is smoothed at the joint 225 which is formed by welding, because the tip 122 g of the second edge portion 122 e is melted in welding. Thus, the tube 122 is provided with the simple ellipse outer shape.

After the two edge portions 122 d and 122 e of the plate member 122B are joined to each other by welding at the bend portion 122 b to form the tube 122, the brazing material layer is formed at the outer surfaces of the plane portions 122 a. The heat-radiation fin 121, the side plate 124, the core plate 111 and the tube 122 are temporarily assembled and integrally fixed, to construct the assembly of the intercooler 100.

In this case, because the outer shape of the tube 122 is the simple ellipse and the core plate 111 is provided with the penetration hole having the simple ellipse shape, the end of the tube 122 can be substantially engaged with the core plate 111 without the large clearance.

The assembly of the intercooler 100 is disposed in the furnace with the same arrangement with the first embodiment, and heated therein to be brazed. In the tube 122 having the joint 225 formed by welding, the inner fin 123 is joined to the inner surface of the tube 122 by brazing through the brazing material. That is, the joining process of the inner fin 123 is performed.

According to the second embodiment, at the tube 122 of the intercooler 100, only the bend portion 122 b at the one end (of width direction) of the tube 122 is provided with the joint 225 that is continuous in the longitudinal direction of the tube 122. The width direction of the tube 122 corresponds to the major axis direction of the cross section thereof having the substantial ellipse shape. Before the forming of the joint 225, the inner fin 123 is arranged in the tube 122. Therefore, the arrangement performance of the inner fin 123 is improved. Because the single joint 225 is provided for the tube 122, the joint reliability of the tube 122 can be bettered.

Moreover, in the joining process of the inner fin 123, the brazing material which has not been used by the brazing will drop due to the weight thereof to be accumulated at the tip 122 f of the first edge portion 122 d, so that a satisfactory fillet is formed. Thus, the joining strength of the joint 225 between the first edge portion 122 d and the second edge portion 122 e can be heightened.

That is, the joint 225 which is formed by welding is reinforced by brazing at the bend potion 122 b of the tube 122. Thus, the reliability of the joint 225 is enhanced.

Moreover, the plate member 122B constructing the tube body 122A is overlapped at the joint 225, and the outer surface of the plate member 122B is smoothed in the welding. The penetration hole of the core plate 111 is formed to have the simple ellipse shape. Thus, the accuracy of the engagement of the tube 122 with the core plate 111 can be improved. Therefore, the fluid leakage from the joint between the tube 122 and the core plate 111 can be restricted.

Other Embodiment

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

In the first embodiment, when the first edge portion 122d of the plate member 122B is temporarily fixed to the second edge portion 122 e thereof by swaging, the tip 122 g of the second edge portion 122 e is plastically deformed to be prolonged so that the outer surface of the plate member 122B is smoothed. However, the temporary fixing process and the outer surface smoothing process can be also separately (respectively) performed.

The fluid passage defined by the tube 122 therein can also have, for example, a rounded-rectangle shape or the like.

Furthermore, in the above-described embodiments, the plate member 122B is overlapped at the bend portion 122 b disposed at the one end of the tube 122. However, the overlap of the plate member 122B can be also omitted, provided that the temporarily fixing and the strength of the bend portion 122 b can be ensured.

In the above-described embodiments, the intercooler 100 is described as an example of the heat exchanger. However, the heat exchanger and the manufacturing method thereof according to the present invention can be also suitably used for other heat exchanger, for example, an oil cooler.

Such changes and modifications are to be understood as being in the scope of the present invention as defined by the appended claims. 

1. A heat exchanger comprising: at least one tube, which is constructed of a plate member and defines therein a fluid passage having a substantially ellipse-shaped cross section; and at least one inner fin, which is arranged in the tube and joined to the tube by brazing, wherein the tube has a single joint, through which the plate member is integrally joined, the joint being continuous in a longitudinal direction of the tube and positioned at a major-axis direction end of the tube.
 2. The heat exchanger according to claim 1, wherein the plate member is overlapped at the major-axis direction end to construct the tube.
 3. The heat exchanger according to claim 2, wherein the tube is arranged so that the major-axis direction end thereof is positioned at an upstream side of an exterior fluid.
 4. The heat exchanger according to claim 1, wherein the tube is integrally joined at the joint, and has a smoothed outer surface at the major-axis direction end of the tube.
 5. The heat exchanger according to claim 4, wherein: the plate member which is temporarily fixed by swaging is integrally joined by brazing at the joint; and the plate member is plastically deformed so that the outer surface of the tube at the major-axis direction end is smoothed.
 6. The heat exchanger according to claim 4, wherein: the plate member is integrally joined by welding at the joint; and the plate member is melted so that the outer surface of the tube at the major-axis direction end is smoothed.
 7. The heat exchanger according to claim 1, wherein a thickness of the inner fin is smaller than that of the tube.
 8. The heat exchanger according to claim 1, wherein the inner fin and the tube are made of copper.
 9. A method of manufacturing a heat exchanger having at least one tube, which is constructed of a plate member and provided with an inner fin therein, the method comprising: a forming process for bending the plate member to form a tube body which defines therein a fluid passage having a substantially ellipse-shaped cross section; a first joining process for integrally joining the tube body to form the tube, the tube body being constructed by the plate member at the forming process; an arranging process for disposing the inner fin at a position where the fluid passage defined by-the tube body is to be formed, before the forming process; and a second joining process for integrally joining the inner fin to an inner surface of the tube by brazing, wherein: at the forming process, two edge portions of the plate member are contacted with each other in a longitudinal direction of the tube body, and positioned at a major-axis direction end of the tube body; and at the first joining process, the two edge portions of the plate member are joined to each other.
 10. The method of manufacturing the heat exchanger according to claim 9, wherein at the forming process, the two edge portions of the plate member are laid to overlap each other at the major-axis direction end.
 11. The method of manufacturing the heat exchanger according to claim 10, wherein at the forming process, the tube body is formed so that the major-axis direction end thereof is positioned at an upstream side of an exterior fluid.
 12. The method of manufacturing the heat exchanger according to claim 9, wherein at the first joining process, the tube body constructed by the plate member is integrally joined by brazing to form the tube.
 13. The method of manufacturing the heat exchanger according to claim 12, wherein the first joining process and the second joining process are performed meanwhile.
 14. The method of manufacturing the heat exchanger according to claim 13, wherein the major-axis direction end of the tube body is arranged at a lower side when the first joining process and the second joining process are performed.
 15. The method of manufacturing the heat exchanger according to claim 12, wherein: at the forming process, the two edge portions of the plate member are fixed to each other by swaging; and the plate member is plastically deformed so that an outer surface of the tube body is smoothed.
 16. The method of manufacturing the heat exchanger according to claim 9, wherein at the first joining process, the tube body constructed by the plate member is integrally joined by welding to form the tube.
 17. The method of manufacturing the heat exchanger according to claim 16, wherein at the first joining process, the plate member is melted so that an outer surface of the tube body is smoothed.
 18. The method of manufacturing the heat exchanger according to claim 16, wherein the major-axis direction end is positioned at a lower side when the second joining process is performed.
 19. The method of manufacturing the heat exchanger according to claim 9, wherein a thickness of the inner fin is smaller than that of the plate member.
 20. The method of manufacturing the heat exchanger according to claim 9, wherein the inner fin and the plate member are made of copper.
 21. The method of manufacturing the heat exchanger according to claim 9, wherein before the forming process, a paste-like brazing material is applied to the plate member which is formed into the tube body. 